(3c) PM2.5 Modeling Challenges

Air Dispersion Modeling is usually required to demonstrate compliance with the Ambient Air Quality Standards for PM_2.5 in support of an air permit application.  These standards are difficult to meet, and the modeling evaluation can quickly become very complicated.  This document and the corresponding presentation are intended to help explain the Prevention of Significant Deterioration (PSD) modeling procedure and shed some light on the methods that can be used to limit modeled concentrations of PM_2.5.EPA has provided some insight and option on several modeling options that could potentially reduce PM_2.5 impact concentrations from sources that have a variable load as well as problem impacts on public roadways.  These items and other ways to potentially reduce modeled PM_2.5concentrations will also be discussed.

 Also looming on the horizon is the requirement to evaluate secondarily formed particulate (from sulfates and nitrates) along with the current primary PM_2.5 evaluation.  EPA’s progress on this upcoming requirement will be reviewed and a preview of what to expect will be provided.